Have been having a difficult-to-diagnose (for me, anyway) problem with my 1991 740 Turbo wagon. Here is what has been happening over the past year, and I'll try to keep it short and to the point. Would very greatly appreciate any help or ideas you can provide as I am lousy at diagnosis.

A year ago replaced left front tire because it had a bubble in it. There was also a great deal of wear on only the outer edge of the tire, somewhat scalloped. The steering wheel also shimmied or jiggled back and forth about 1 inch or so. Putting a new tire on seemed to fix everything. However, I had a gut feeling it was not really fixing the underlying problem.

Slowly, over the past year, the steering wheel shimmy has returned and progressively gotten pretty bad. The whole car shook with it at times. The new tire is now fully worn out on the outside edge of the tread. It is also scalloped like the one it replaced. There is no bubble this time.

Because I am so bad at diagnosis (and I have read the 700/900 series FAQ for steering and front suspension), I took it to a local Volvo mechanic, not the dealer. He said that the problem was the tire, and swapped it with the left rear (they are directional tread and he could not cross-rotate them). He was wrong. On the way home, the steering wheel shimmy was there as bad as ever. The car does not shake as badly, but I think it is because the old, scalloped tire is not on the front contributing to the problem. But, the tire that is there will soon wind up scalloped.

The mechanic claimed that he put the car on a rack and pulled and pushed, etc. the tire/wheel and that my ball joints/bushings/tie-rod ends are all fine. But I think he is wrong (and possibly an idiot). Something other than the tire has to be making the wheel shimmy, and causing two tires in succession, at the same corner of the car, to wear exactly the same way: outside edge wear only, with scalloping or cupping. Kind of sawtooth wear, but much further apart than saw blade teeth.

Am I right, and should I just methodically work through the diagnosis in the FAQ. And any extra insight or refinement to the diagnostics that you can provide, I would love.

Thanks
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Scott Cook - 1991 745T, 1985 RX-7 GSL-SE, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)